Total Synthesis of Starfish Cyclic Steroid Glycosides. Part 3, Formal Total Synthesis of Luzonicosides A and D

Abstract

Comprehensive SummaryLuzonicosides A (1) and D (2) are the major saponins isolated from pacific starfish Echinaster Luzonicus, featuring a sterically congested 16‐membered ring which is formed by bridging the C3 and C6 of a 3β,6β‐dihydroxy‐Δ7‐ene steroid with a 1,2‐trans‐linked linear trisaccharide via glycosidic and ether bonds, respectively. Here, we describe a formal total synthesis of starfish cyclic steroid glycosides 1 and 2. The synthetic route is highly modular and versatile, involving construction of the 16‐membered macrocycles via Au(I)‐catalyzed intramolecular glycosylation, highly efficient installation of unsaturated sugar moieties with ortho‐hexynylbenzoates, elaboration of glucuronic acid unit via post‐oxidation, and a de novo synthesis of the ether‐linked pyranose unit.